The bold texts are themselves another assumption (of a war with clear and measurable goal). But is't right? Military action is just extension of politics and another one of many political means to achieve political goals. To me the only goal in Russia's mind which is certain is to keep Ukraine as a buffer like China keeping Korea from falling to full US control or Vietnam fully falling to USSR. That kind of goal does not necessarily demand a clean victory. Korean war ended in a cease fire and technically can resume any time. Vietnam and China kept fighting at the border more than ten years after 1978's war. Why then do people expect that Russia would expect or could finish the matter with a clean cut victory in any sort? If that is clear to the Russian leadership and is their expectation and intension, why should people here expect anything else? This is why I said "people should not project their own unrealistic exceptions on others".
Another way to express my view. Achieving a quick and clean victory in early stage as many people here expected, is great for Russia. And Russian leaders will certainly not reject it. But is the Russian leaders really expect this as the only outcome without doubt and without preparing for a less rosy but more realistic outcome? If it is the last, I don't see any major error in decision making. Put it simply, I prepare for long but would be happy for the short and glory, no matter what. From a strategic point, pure military performance is just academics and irrelevant to the end goal which is determined by industrial capability and will.